1. Field of the Invention
The present invention relates to the field of machine tools and more particularly to modifications with which high-speed displacements along three axes X, Y and Z of a slide carrying the movable machining tool can be achieved under the best conditions.
2. Description of the Related Art
High-speed machining of parts in a machine tool generally takes place using rotary tools installed at the end of a slide, which itself is mounted to be movable along three axes, two of which X, Y are disposed in a plane P(x,y) parallel to the plane of machining of the parts and the third Z is disposed in a plane P(x,z) perpendicular to the same plane of machining of the parts.
To facilitate reading of the description to follow, the plane of machining of parts will be assumed to be vertical, as is the case in the majority of embodiments of machine tools of this type in the field of high-speed machining, and so the plane P(x,y) of the first two axes X and Y is considered to be vertical and the plane P(x,z) of the third axis Z is considered to be horizontal.
A machine tool for high-speed machining is generally provided with three main working stations, to wit:
a machining station proper, provided with the tool driven rotationally at the end of the slide and shaping the part to be machined, PA1 a drive station situated after the machining station and comprising an assembly of mechanisms that ensure in particular the X, Y and Z displacements of the slide, which also ensures the rotary movement of the tool carried at the end, and PA1 a control station cooperating with the drive station as a function of a program of instructions preestablished to organize and take charge of the different phases of machining of the part. PA1 two parallel guide rails in the horizontal plane P(x,z) to enable the transverse horizontal displacements of the slide along the X axis, PA1 two parallel guide rails in the vertical plane P(x,y) to enable the vertical displacements of the slide along the Y axis and perpendicular to the X axis, PA1 two parallel guide rails in the horizontal plane P(x,z), perpendicular to the rails for transverse horizontal displacements along the X axis, to enable the horizontal longitudinal displacements of the slide along the Z axis, perpendicular to the X and Y axes. PA1 two transverse guide rails disposed in parallel in the vertical plane P(x,y) enable the transverse horizontal displacements (arrow X) of the slide along the X axis, and PA1 two lateral guide rails disposed in parallel in the same vertical plane P(x,y), enable the vertical displacements (arrow Y) of the slide along the Y axis, perpendicular to the X axis. The two structures differ in that the structure described by the European Patent is not provided with rails or slide blocks permitting it to move its tool perpendicular to the plane P(x,y), or in other words along the Z axis. Instead, the part holder is provided with a kinematic linkage permitting it to move to and fro perpendicular to the plane of movement of the slide. PA1 The logical structure ensures guidance on four slide blocks for movement along the Y axis and Z axis, and these four slide blocks require that the logical structure adopts for these very two movements an orthogonal geometry, which makes the structure heavy and increases its volume. The choice of a device of the ballscrew type as means of movement in fact necessitates the presence of a large number of guides to avoid jamming and to gain in precision. PA1 This choice of actuators has the disadvantage not only that the logical structure is necessarily heavier but also that it cannot meet the needs inherent to high-speed machining. Thus, the movements between the different machining steps (tool-changing or tool-placing movements) must be ultra-fast, which is not possible with this logical structure because of its heavy weight. In addition, a drive of the ballscrew type does not always provide the precision required for modern machining operations. PA1 an appreciable increase in rigidity of the logical structure, PA1 closer proximity of the movable masses to a vertical plane, PA1 much smaller floor space requirement, and PA1 an opportunity to make the structure of the support elements of the guide rails lighter. PA1 the access and/or unloading area to be disposed at the right or left of the machine, PA1 a plurality of machines to be coupled side-by-side, and PA1 a smaller floor space requirement on the order of 1600 mm wide to be achieved, thus enabling integration of the machine into a transfer unit with a spacing of 800 mm.
In such machine tools, the logical structure of the machine is built substantially around the drive station and in particular as a function of the arrangement of rails guiding the reciprocating rectilinear displacements of the slide along the three axes X, Y and Z. The traditional design of the frame of such a machine comprises disposing:
Within the context of the invention, the transverse and longitudinal displacements X and Z respectively of the slide are understood as being relative to the longitudinal axis of the machine, along which there are aligned the three working stations.
Although such an arrangement is not currently the subject of any development in the field of machine tools, this nondevelopment is because translational movements of the movable mechanisms are generally driven by rotating electric motors cooperating with belts and gears to convert the rotary movements into linear movements. In addition, since the problem of a floor space requirement of machine tools is not the main concern of the manufacturers, this triaxial logical arrangement has never been questioned, because it offers more convenient seating of the frame on the floor, especially when the mechanisms making up the machine tool, such as tool cassettes, motors, etc. are cumbersome and heavy.
A new machine concept has been to provide machines in which the two horizontal rails enabling the displacements (arrow X) along the X axis are disposed in parallel and one above the other in the plane P(x,y). The machine tools described in European Patent No. 0614724 and in German Patent No. 3704952 provide such a logical structure in which:
The structure proposed by German Patent No. 3704952 proposes a tool movement along the Z axis, but in a manner that, for several reasons, is particularly inadequate for high-speed machining. On the one hand, the tool is located at the end of an arm which is telescopic in the Z axis and which, although easy to employ as a means used for a particularly large machining travel in the case of a normal tool and drive, is much more difficult to apply for the movement of a tool-carrying electric spindle because of its weight (and consequently of the overhang), of the hydraulic and electric connections for tracking its movements and of the much shorter travels required of it. On the other hand, this telescopic arm enables movement in the Z direction and occupies space of the logical structure only on a single half plane or half Z axis, which has the consequence of increasing the volume of a machine that uses such a structure.
Another difference existing between the two cited logical structures lies in the fact that the structure proposed by European Patent No. 0614724 adopts linear motors as drive means in order to ensure displacements of the slide along the two axes X and Y and of the part holder along the Z axis. Such motors are particularly suitable for achieving the rapid and precise movements required by modern machining. Nevertheless, the slide of the logical structure of that patent is fixed relative to the Z axis, and it is the part-holder module which, by means of linear motors, is displaced or becomes distant from the slide and its tool. The absence of movement along the Z axis is a particularly serious limitation for such a machine.
Another machine design described in U.S. Pat. No. 4,752,160 uses three pairs of rails disposed perpendicular to each other in order to enable displacement of the tool along the two axes X and Y, from one working station to another aligned along the X axis, one on each side of a control station.
The displacement of the tool is enabled according to the embodiment, which is illustrated in two ways. On the one hand, the logical structure carrying the tool and enabling its displacement along the Y axis is displaced on a central portion of rails situated opposite the control station and mounted to be detachable relative to the remaining lengths in order to displace the tool toward the control station along the Z axis, but only on this portion of detachable length of the X axis. On the other hand, the tool carriage is displaced along the Z axis by slide blocks, on which it slides, driven by a ballscrew device moved by a motor connected to the slide.
Although this patent proposes a kinematic structure enabling displacement of the tool on three axes, it exhibits several disadvantages, such as: